Relationship between TR jet velocity and cell free hemoglobin. (A) The nonlinear relationship between tricuspid regurgitation velocity (TR jet velocity) and cell free hemoglobin for all subjects; at higher cell free hemoglobin levels, TR jet velocity is higher across all 3 groups. (B) A higher proportion of patients with cell free hemoglobin levels >10 mg/dL (elevated) has a TR jet velocity >250 cm/s, above which portends increased risk of mortality in SCD. (B inset) A 2 × 2 table showing relative risk assessment of plasma free hemoglobin >10 mg/dL for TR jet >250 cm/s.